The 3GPP-standard relates to technology based on radio access networks, such as the UTRAN (the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network), which is a radio access network architecture providing W-CDMA (Wideband Coding Division Multiple Access) to mobile terminals, which in the 3GPP are referred to as UEs. Telecommunication systems according to the 3GPP-standard offer higher and variable bit-rates and are capable of providing new types of services to the users. The MBMS included in the 3GPP-standard provides broadcasting/multicasting of various multimedia information to users, enabling information providers to transmit multimedia information, such as real-time audio and video, still images and text, e.g. news, sport results and weather forecasts, to several joined MBMS subscribers simultaneously.
In a telecommunication system according to the 3GPP-standard, a UE, i.e. a mobile terminal, such as e.g. a cellular telephone provided with a SIM (Subscriber Identity Module)-card, communicates with a core network connected to external networks, e.g. the Internet and the PSTN (the Public Switched Telephone Network), via a UTRAN covering a geographical area divided into cells with unique identities. Each cell is served by a base station device, which in the 3GPP is referred to as a Node B, and the radio coverage of a cell is provided by a base transceiver station at the serving base station (i.e. Node B) site over an Uu-interface. One Node B is normally serving more than one cell, and the Node Bs are controlled by RNCS (Radio Network Controllers), which are managing important transmission resources of the UTRAN and are connected to one or more core networks. The Node Bs are communicating with the RNCs over an Iub-interface, the RNCs are communicating with the core network over an Iu-interface, and the communication between RNCs is performed over an Iur-interface. The UTRAN interfaces (Iu, Iub and Iur) have one control plane and one user plane, and the RNSAP (Radio Network Sub-system Application Part) is a control plane protocol for the Iur-interface.
A network architecture for providing an MBMS data stream to a number of MBMS-joined mobile terminals (UEs) located in cells served by a common Node B comprises a BM-SC (Broadcast/Multicast-Service Center) as a source for scheduling the MBMS data streams for delivery to a Serving GPRS Support Node (SGSN) using suitable transmitting means, the SGSN being configured with a Gateway GPRS Support Node (GGSN). An RNC supervising the Node B, i.e. a controlling radio network controller (CRNC) receives the MBMS data stream from the SGSN for transmission to the Node B over an Iub interface, and the Node B forwards the MBMS data stream over an air interface (i.e. Uu-interface) to the MBMS-joined UEs located in the cells served by the Node B.
In a radio access network (RAN), such as the UTRAN, a radio network controller (RNC) will function as a Serving RNC (SRNC) for a specific UE, while the UE is connected to the RAN, also when the UE moves over a large geographical area and passes through several cells, until the UE is disconnected from the UTRAN, e.g. at power off, or when the UE is converted to an idle mode due to inactivity, i.e. an RRC Connection Release. An RNC to be functioning as an SRNC for a specific UE will receive an Iu-link from the core network comprising information regarding the UE, create a UE context and store the received information regarding the UE therein. A UE context indicates the cell location of said UE and information regarding the connection of the UE between the core network and the radio network via the Iu interface. The RNC functioning as an SRNC for a UE will control the connection of the UE within the radio access network until the UE is disconnected at power off. If the UE relocates to a cell controlled by a second, different RNC than the SRNC, the SRNC will send a link forwarding the UE information over the Iur-interface (i.e. an Iur-link) to said second RNC, which will store the linked UE information and function as a drift RNC (DRNC) regarding said UE, while the UE is located in any of the cells controlled by said second RNC. However, an RNC will always function as a Controlling RNC (CRNC) for the UEs located in the cells served by the Node Bs connected to it via the Iub interface, and the CRNC will control the radio resources for those cells. Thus, a physical RNC will normally contain SRNC, DRNC and CRNC functionalities, and will function as either a SRNC/CRNC or a DRNC/CRNC for a specific UE. Regarding the radio resource control (RRC), the UE operates either in an Idle Mode or in a Connected Mode, and the UE automatically enters the Idle Mode at power on, before a connection is established between the UE and a UTRAN. When a connection is established, the UE enters a Connected Mode, and is assigned a U-RNTI (a UTRAN Radio Network Temporary Identity), which can be used in any cell of UTRAN. Within the Connected Mode, there are four different states, i.e. the CELL_DCH (Dedicated Channel) state, the CELL_FACH (Forward Access Channel) state, the CELL_PCH (Paging Channel) state and the URA_PCH state. In the CELL_DCH state, a dedicated traffic channel is allocated to the UE, in the CELL_FACH state the UE monitors a common channel (the FACH) continuously in the downlink of the selected cell and uses a RACH (Random Access Channel) as uplink, and in the CELL_PCH state the UE monitors a paging channel of a selected cell. The cell location of UEs in any of these states is stored in the UE context in the SRNC, and at cell relocation, the UE will update the UE context in the SRNC with its new cell location by sending a cell updating message to its SRNC. However, while a UE is in the fourth connected state, the URA_PCH state, the exact cell location of the UE will not be stored in the UE context in the SRNC. Instead, the UE context will contain information regarding the location of the UE only at a cell group level, i.e. regarding which URA (UTRAN Registration Area) the UE is located in. A URA may span over cells served by Node Bs connected to different RNCs, and the UE will update the UE context with its new URA location only when crossing a URA border by sending a URA updating message to the SRNC.
The relationship between a service provider of an MBMS multimedia service according to the 3GPP and a user, i.e. a mobile terminal, which in the 3GPP normally is referred to as a UE, is established as an MBMS subscription, allowing the user to receive the related MBMS information. When a user wishes to receive MBMS information, he activates the MBMS, indicating to the radio access network that he is prepared to receive multimedia information associated with a specific MBMS. Thereby, he joins a multicast group for reception of a MBMS data stream transmitted by multicasting, and MBMS information regarding the TMGI (Temporary Multicast Group Identity) is added to the UE context in the SRNC, thereby creating an MBMS UE context. When the user no longer wishes to receive any MBMS information, he deactivates the MBMS and resigns from the multicast group.
In transmission by multicasting, two different transmission schemes may be used to transmit the data stream in a cell, either the point-to-point (PTP) scheme or the point-to-multipoint (PTM) scheme, depending on the number of users located in the cell. In transmission according to the PTP scheme, the data stream is delivered to each user individually, using a dedicated traffic channel, and in transmission according to the PTM scheme, the same data stream is sent on a common channel, which can be received simultaneously by a plurality of UEs. The PTM scheme is advantageous when the number of receivers in a cell is large, and the PTP scheme is advantageous when only a few receivers are located in the cell. Transmission according to the PTM scheme avoids duplication of the same content on different radio bearers, thereby saving transmission resources, while the transmission power overhead required for transmission on a common channel is avoided by transmission according to the PTP scheme. Therefore, the allocation of the available radio resources can be optimised by counting of the MBMS-joined UEs located within each cell and selecting between the PTM scheme and the PTP scheme in a so called PTP/PTM transmission decision, which is based on the result of said counting procedure.
When a UE subscribing to an MBMS service has activated the MBMS and joined an MBMS multicast group, the identity of the temporary MBMS multicast group is stored in the MBMS UE context in the SRNC, as well as in the SGSN. An MBMS service provider will initiate an MBMS session by sending an MBMS session start notification to inform the joined UEs in the multicast group that an MBMS data stream will be transmitted. In order to decide whether to use the PTP scheme or PTM scheme in the multicasting of the MBMS data stream, the controlling radio network controller, CRNC, will perform a counting procedure of all MBMS-joined UEs located within the cells served by the Node Bs supervised by each CRNC. The result of the counting serves as a basis for the PTP/PTM transmission decision, i.e. it is used by the CRNCs to select the PTM scheme or the PTP scheme for transmission of an MBMS data stream to MBMS-joined UEs located in each cell controlled by the CRNC.
The counting of MBMS-joined UEs in a Connected mode in a specific cell is normally performed by counting the MBMS UE contexts indicating the specific cell location. More specifically, the counting of MBMS-joined UEs for a PTP/PTM transmission decision is performed by the CRNC updating cell counters for each cell, either a separate cell counter for each UE state, or one common cell counter. The cell counters for each cell are updated according to a pre-defined cell counter updating procedure, and before transmitting the MBMS data stream in a cell, the CRNC compares the value of the corresponding cell counter or cell counters with an operator-defined threshold value. Following the comparison, PTM-transmission in a cell is selected if the value of the corresponding cell counter is approximately above said threshold and otherwise PTP-transmission is selected. A prior art cell counter updating procedure for a PTP/PTM transmission decision before MBMS multicasting may e.g. comprise updating the cell counters after counting of MBMS UE contexts indicating the specific cell location, updating the counters at a received MBMS UE link from the core network or from an SRNC indicating the specific cell location, by dedicated paging of certain UEs and updating the counters accordingly, and by counting by notification, which involves updating the counters after receiving a Cell Update-message from a UE as a response to an MBMS notification of a MBMS session start. The step of counting the MBMS UE contexts is applicable to most UEs in the Connected mode, but gives only a fractional counting of Connected mode UEs in the URA_PCH state and in the Idle mode. Therefore, counting by notification or counting by paging is normally required for Idle mode UEs and for Connected mode UEs in the URA_PCH state. Counting by notification is not applicable for UEs in the CELL_DCH-state, which must be counted by counting of UE contexts or by UEs links received from the core network over the Iu-interface or from a serving RNC over the Iur-interface. The combination of the counting procedures described above depends on the state of a UE and on the operator, and hereinafter cell counter updating triggered by counting of MBMS UE contexts or by receiving MBMS UE link is defined as counting by linking, and cell counter updating triggered by receiving a response to dedicated paging of a UE or to an MBMS session start notification is defined as counting by paging.
At the start of an MBMS session and during a session, counting by linking, i.e. counting of the UE contexts and of UE links, gives the exact number of UEs in a cell in the Connected state. However, the UEs in the URA_PCH state are not counted accurately by this method, since the exact cell location is unknown for these UEs. Only an estimated number of UEs per cell can be calculated, e.g. by means of a fractional counting procedure, by calculating the number of URA_PCH mobiles in the URA divided with total number of cells in the URA. Another counting procedure involves an estimation of the number of UEs, assuming that each UE is still located in the cell from which the last message was sent to the network. The UEs in the Idle mode can also, optionally, be counted by means of fractional counting, as a fractional number per cell and registration area calculated by the CRNC, based on the number of UEs interested in MBMS, which is received at session start from the core network and is updated during session.
One drawback with prior art cell counter updating procedures is that neither counting by linking nor counting by paging are completely accurate. In counting by paging for a retransmission of an MBMS session, i.e. a repetition, errors will occur, e.g. since a UE will not respond to counting by notification if it has already received a MBMS session correctly, and since a cell update sent as a response to counting by notification does not include any MBMS ID. An important drawback with counting by paging is that it involves dedicated paging of UEs, which increases the signaling load over the Uu interface, and requires more transmission resources than counting by linking. Another drawback in prior art cell counting procedures is that certain factors are not considered in the PTP/PTM transmission decision, such as repetition of the MBMS session, the reception in PTP-mode and the predicted reception of a transmitted MBMS session in the PTM-mode. In order to indicate a repetition of an MBMS session, i.e. a retransmission of an MBMS data stream, an MBMS session ID, indicating the version of a specific multimedia service, can be stored in the MBMS UE context regarding each transmission, in association with the MBMS service ID. However, the retransmission can only be detected in case the retransmission is performed by the same RNC as the original transmission.
Therefore, the aim of the present invention is to solve the problems described above relating to counting of the multimedia service joined mobile terminal located in a cell for the PTP/PTM transmission decision, especially of UEs in the 3GPP, to be able to optimise the PTP/PTM transmission decision performed by the CRNC before the multicasting of a multimedia service stream in a cell, thereby optimising the radio resource allocation.